This invention relates to plural-wavelength infrared detector devices including first and second detector elements comprising respective first and second infrared-sensitive semiconductor materials of different bandgaps, each detector element comprising a p-n junction. More information about the wavelength characteristics of an object or a scene can be obtained by viewing it using such a plural-wavelength infrared detector device so that, for example, such a device can permit the temperature of a radiation source to be measured independent of the emissivity of the source and the transmission of the intervening space. The different bandgap materials may be provided as different levels on a substrate.
Published European patent application EP-A-0 087 842 which corresponds to U.S. Pat. No. 4,555,720 discloses a plural-wavelength infrared detector device comprising upper and lower levels of infrared-sensitive semiconductor material provided on a substrate. The lower level is located between the upper level and the substrate and insulated from the upper level by an intermediate insulating layer. A detector element is formed in each level, and each detector element may comprise a p-n junction between opposite conductivity-type regions of the semiconductor material. Electrical connections are present from the detector-element regions to the substrate. The semiconductor material of a first of the upper and lower levels has a smaller bandgap than the second of the levels so as to provide its detector element with a response to a longer infrared wavelength. The substrate may be, for example, an insulating support carrying conductor tracks, or the substrate may be, for example, a silicon integrated circuit for processing the output signals from the detector elements. The whole contents of EP-A-0 087 842 are hereby incorporated herein as reference material.
An advantageous connection structure for the upper-level detector element(s) is disclosed in EP-A-0 087 842. In this structure, the upper level bridges a gap in the lower level between the lower-level detector element(s) and a separate part of the lower-level material; this separate part comprises or carries the connection to the upper level, for example as metallization on a side-wall of the separate part. Specific embodiments are described in which the lower-level material has the smaller bandgap so that its detector element has a cut-off wavelength of approximately 11 .mu.m (micrometers); the connections to the smaller-bandgap detector element(s) are formed entirely in the lower level and before providing the upper-level material.